Advances in plasma processing have facilitated growth in the semiconductor industry. The semiconductor industry is a highly competitive market. The ability for a manufacturing company to be able to process substrate in different processing conditions may give the manufacturing company an edge over the competitor. Thus, manufacturing companies have dedicated time and resources to identify methods and/or arrangements for improving substrate processing.
In general, plasma processing systems may be constructed from a plurality of configurations. For example, a plasma processing system may be configured as a capacitively-coupled plasma (CCP) processing system or an inductively-coupled plasma (ICP) processing system. Each plasma processing configuration is built to enable processing in a range of process parameters.
However, in recent years, the types of devices that are being processed have become more sophisticated and may required more process control. In an example, devices being processed are becoming smaller and may require more precise control of plasma parameters, such as plasma density and uniformity across the substrate, for better yield. Furthermore, device fabrication may be a multi-steps process. Each step in the process may require different process regimes achievable only on plasma processing system of a specific configuration. Thus, the range of process parameters of a plasma processing system from a single configuration may fall short of delivering a total solution to process next-generation substrates.
To facilitate discussion, FIG. 1A illustrates a simplified representation of a prior art capacitively-coupled plasma (CCP) processing system. Plasma processing system 100 may be a single, double (DFC), or triple frequency radio frequency (RF) capacitive discharge system. In an example, radio frequencies may include, but are not limited to, 2, 27 and 60 MHz. Capacitively-coupled plasma processing system 100 may be configured to include a substrate 106 being disposed above a lower electrode 102.
Consider the situation wherein, for example, substrate 106 is being processed. During plasma processing, an RF generator 108 with a path to ground may supply an RF power to lower electrode 102 through an RF match 110. In an example, RF match 110 may be used to maximize power delivery to the plasma system. The power from RF generator 108 may interact with a gas (not shown to simplify illustration) to ignite plasma 114 in a gap 112 between an upper electrode 104 and substrate 106. In the example of FIG. 1A, upper electrode 104 is shown as being grounded. However, upper electrode 104 may also be powered. Plasma 114 may be used to etch and/or deposit materials onto substrate 106 to create electronic devices.
In CCP processing system such as plasma processing system 100 of FIG. 1A, gap 112 may be configured to be a very narrow gap. The gap may be about 1:5 to about 1:15 the aspect ratio of gap 112 to the diameter of upper electrode 104. By having narrow gap, processing steps requiring shorter gas resident time to minimize loading effect may be employed to process substrate. As the term is employed herein, loading refers to a measurable depletion of an active etchant cause by consumption in the etch process. Thus, CCP processing system may accommodate etching of electronic devices with very small features requiring very low gas resident time.
In general, a limiting feature of CCP processing system 100, as illustrated in FIG. 1A, may be the inability to decouple ion density and ion energy. During plasma processing, it may be difficult in CCP processing system to independently control the ion density and the ion energy. For example, an attempt to increase ion energy by increasing RF power may cause an increase in sheath potential leading to an increase in ion energy. Another limiting feature of CCP processing system 100, as illustrated in FIG. 1A, may be the ability to generate high plasma density as compared to inductively-coupled plasma processing system. Thus, CCP processing system may not be able to accommodate plasma processing steps requiring high plasma density and/or independent control of the ion energy and the ion density.
FIG. 1B illustrates a simplified schematic representing a prior art inductively-coupled plasma (ICP) processing system. Inductively-coupled plasma processing system 150 may be configured to include a substrate 156 being disposed above a lower electrode 152. As shown in FIG. 1B, the lower electrode 152 may be grounded or may be powered with a first RF generator 158. RF power to lower electrode 152 may be delivered through an RF match 160. In an example, RF match 160 may be employed to maximize power delivery to the plasma system.
Consider the situation wherein, for example, substrate 156 is being processed. During plasma processing, a second RF generator 168 may supply RF power to an inductor coil 166. The cross section of inductor coil 166, as shown in FIG. 1B, may be a spiral coil with an air core being disposed above a dielectric window 154. The power from RF generator 168 to inductor coil 166 may produce a magnetic field 172 penetrating through dielectric window 154. The induced electric field may generate electrical current that may interact with gas to ignite and maintain plasma 164.
In contrast to the CCP processing system of FIG. 1A, plasma 164 being generated by ICP processing system tends to have higher density at similar RF power levels. One main difference between ICP processing system 150 and CCP processing system 100 may be the way RF power is coupled to plasma. Except for the low bias RF power from RF generator 158 being applied to substrate 156, RF power may be coupled to plasma 164 through dielectric window 154 in ICP processing system 150. Thus, high ion density and low plasma potential may be achieved in ICP processing system by employing efficient, non-capacitive coupling of RF power to plasma.
As shown in FIG. 1B, plasma 164 may have a torroidal/doughnut shape, where the plasma doughnut may be formed between dielectric window 154 and substrate 156 in between a gap 162. The magnetic field 172, as shown in FIG. 1B, may peaked off axis, i.e., half (½) the distance of the radius 170 of inductor spiral coil 166 with minima at the center of the coil and the walls. Thus, the plasma doughnut 164 may have the highest density at about half (½) the distance of the radius 170 of inductor spiral coil 166 due to the magnetic field 172 generated by inductor spiral coil 166.
As may be appreciated by those skilled in the art, the gap 162 in ICP processing system needs to be of a sufficient height, i.e., the height of gap 162 tends to be about the radius of inductor coil 166, to accommodate the magnetic field 172 being generated by inductor coil 166. Sufficient gap height may be necessary such that RF power induced through dielectric window 154 may be absorbed in plasma 164. By having sufficient gap height for plasma to absorb RF power, damages to substrate 156 may be avoided. For example, if the gap is too narrow, magnetic field 172 may interact with substrate 156 to produce electric field inducing current and capacitive coupling instead of producing and/or sustaining plasma. The capacitive coupling may lead to an arcing of the devices on the substrate and/or an increased in temperature on the substrate, which might be undesirable for plasma processing. Thus, ICP processing system may be limited to operating with relatively large gap for plasma processing.
Another limitation with ICP processing system 150, as shown by FIG. 1B, may be in processing of very large substrate. In order to achieve a relatively good uniformity of plasma, as affected by the magnetic field, over a very large substrate, inductor coil 166 may need to be scaled up to the appropriate size. Therefore, the chamber may end up becoming very large because the region of maximum plasma is about half the radius 170 of inductor coil 166. To achieve good uniformity of plasma, the inductor coil 166 may need to be large enough to cover the large substrate and not give rise to non-uniformity at the edges. However, as the chamber becomes enlarged to compensate for the inductor coil, the design of ICP processing system may pose a variety of mechanical and/or engineering challenges. For example, the vacuum load may be very high in order to support the enlarged ICP processing system. In addition, the gas may not be evacuated rapidly enough leading to undesirably long resident time. Furthermore, a larger dielectric window 154 may be more difficult to handle.
Even though ICP processing system may be able to deliver high density plasma and decoupling of ion density and ion energy, ICP processing system may be limited to relative large gap and design challenges resulting from compensating for plasma uniformity when processing larger substrates.
FIG. 2 shows a simplified schematic of prior art inductor coils arrangement as proposed by V. Godyak in “Distributed Ferromagnetic Inductively Coupled Plasma as an Alternative Plasma Processing Tool”, Japanese Journal of Applied Physics Vol. 45, No. 10B, 2006, pp. 8035-8041.
As shown in FIG. 2, a plurality of cores 202A, 202B, 202C, 202B, 202E, and 202F may be employed. In contrast to the air core of FIG. 1B, each core may be constructed of a magnetic material such as ferrite or powder iron. Each core from the plurality of magnetic cores (202 A-F) may be configured with a coil from a plurality of coils 204A, 204B, 204C, 204D, 204E, and 204F to act as small inductor sources. For example, as shown in FIG. 2, coil 204A corresponds to the winding for magnetic core 202A. The magnetic core materials may be employed to confine the magnetic field to a region to improve coupling, in contrast to FIG. 1B, where the coil may be a spiral arrangement to induce a torroidal/doughnut shape magnetic field from the current from the coils. Thus, the arrangement of a plurality of small inductor cores may address the spatial uniformity problem of a single, large spiral coil of FIG. 1B.
As shown in FIG. 2, the inductor cores (202 A-F) may be wound with coils (204 A-F) and connected in series in a hexagonal close packing arrangement to improve uniformity and increase efficiency of magnetic coupling. However, the hexagonal close packing arrangement is employed as a space filling for the inductor coils without any attempt to coordinate these core elements.
As may be appreciated from the foregoing, CCP processing system may be limited to low density plasma and/or inability to decouple the ion density and the ion energy. Even though ICP processing system may be able to overcome the limitations of generating high density plasma and/or decoupling of ion density and ion energy, ICP processing system may be limited to relatively large gap and/or design challenges when processing larger substrates. Given the need to stay competitive in the semiconductor industry, enhancements to the capabilities of CCP and ICP processing systems are highly desirable.